Direct Substitution of Alcohols in Pure Water by Brønsted Acid Catalysis

Abstract

With the increasing concern for sustainability, the use of environmentally friendly media to perform chemical processes has attracted the attention of many research groups. Among them, the use of water, as the unique solvent for reactions, is currently an active area of research. One process of particular interest is the direct nucleophilic substitution of an alcohol avoiding its preliminary transformation into a good leaving group, since one of the by-products in this approach would be water. The direct substitution of allylic, benzylic, and tertiary alcohols has been achieved through SN1-type reactions with catalytic amounts of Brønsted or Lewis acids; however, organic solvents are often required. In this review, the pioneering SN1 approaches performed in pure water and in the absence of a metal based Lewis acid are compiled and discussed.

Ultrasound-assisted multicomponent synthesis of 4H-pyrans in water and DNA binding studies

“…Furthermore, the advantages of using water would be in agreement with some of the twelve principles of Green Chemistry [40][41][42][43][44] . However, despite the number of processes that have been investigated and developed in water, maybe because of the good solubility of reactants is generally considered a prerequisite for an appropriate reactivity, water is still not commonly used as a sole solvent for organic reactions [45][46][47][48][49] . For all these reasons, the development of reactions in pure water is still a challenging task.…”

Nonclassical Mechanism in the Cyclodehydration of Diols Catalyzed by a Bifunctional Iridium Complex

“…[18] In an attempt to obtain furthere videncef or the formation of carbocationics peciesi nt he cyclodehydration of diol 2b,w e carriedo ut an umber of experiments in the presence of nucleophiles (see the Supporting Information). [19] With diol 2b as a substrate, these experimentso nly resulted in the formationo f tetrahydrofuran 3b.However,when amodel alcohol with identical electronic properties that is unable to undergo intramolecular cyclization, namely 1-(p-methoxyphenyl)-1-pentanol (13 b), was subjected to the same reaction conditions, this substrate did react with the added nucleophiles( e.g.,M eOH, 5equiv). This result clearly supports the idea of carbocationic intermediates in the cyclization of diol 2b.…”

Lewis Acid‐Catalyzed Nucleophilic Substitutions of Benzylic Alcohols with Sulfamides

“…It is well established that the nucleophilic substitutions of alcohols, catalyzed by Lewis acids or Brønsted acids, proceed via carbocations following the S N 1 mechanism. [16] However, we found that the reaction proceeded with difficulty for steric hindered substrates, such as 6 c. Thus, to verify the reaction pattern, we carried out the reaction using enantiopure (R)-5 a as a starting substrate (Scheme 5, (1)), for which the product 6 a was obtained in 94 % yield as a racemate; therefore, the reaction was found to follow S N 1 mechanism in this case as well. In addition, the homoether was reacted to give the sulfamide 2 a in 95 % yield (Scheme 5, (2)), thus confirming the homoether as an intermediate, as observed by TLC analysis.…”

“…In recent years, nucleophilic substitutions of alcohols catalyzed by Lewis acids or Brønsted acids have gained increasing attention as methods with high atom efficiency and environmental friendliness (Scheme 2a). [16] A number of nucleophiles have been applied to the reaction system, and useful characteristic reactions have been reported. Although there are many reports on the nucleophilic substitutions of alcohols using sulfonamides as a nucleophile, [17][18][19] there are few reported examples of the application of sulfamides for such a reaction.…”